In larger boring, milling and the like machine tools, the spindle has for the transmission of the drive forces onto the tool a conical receiving bore, which is as large as possible, for receiving a tool with a conical shaft, which is as large as possible, for example an ISO 60 7/24 shank. However, on such modern large machine tools also precision work (like boring, milling and thread-cutting) with smaller tools must be carried out. It is thus necessary to provide a tool holder which can be inserted into the conical receiving bore of the spindle, which tool holder itself also has a conical receiving bore but of smaller dimensions, for receiving a smaller conical shaft, for example an ISO 50 7/24 shank of a tool. Such tool holders, which permit the use of tools with smaller conical shafts than the spindle-receiving bore, are also known as reducers, adapters or intermediate pieces. In a known tool holder of the above-mentioned type (shown in a brochure of the Firm Forkardt entitled "Schnellwechsel-Werkzeughalter System Erickson" ("Quickchange tool holder System Erickson") and published in 1978), the support member has on its outer periphery a thread, onto which is screwed a retaining nut. Said nut is provided with two inwardly projecting fingers, which can move through the keyways of a flange provided on the tool following the conical shaft. Upon rotation of the nut, the fingers rest on the outside of the flange and pull the tool conical shaft into the receiving bore of the support member. The nut thus serves as a type of clamping mechanism for clamping the tool conical shaft in the receiving bore of the support member. Aside from the fact that with the help of such a nut only relatively small clamping forces can be applied, which are not sufficient for the large machine tools, this known tool holder is also not suited for an automatic tool exchange.
The basic purpose of the invention is to produce a tool holder for boring milling and the like machine tools of the above-mentioned type, which, with minimum expense and high reliability and in a small (in particular small axial) space, permits an automatic exchange of tools with a high clamping force and also a high ejecting force, such tool holder itself being automatically exchangeable in a simple manner on the machine tool spindle, if desired.
This is attained according to the invention by the tool holder conical shaft having a coaxial bore, in which is axially movable a collet carrier with a collet, the ends of which collet are constructed as claws and engage an annular groove at the free end of the tool conical shaft; by arranging in the support member, concentric with the second conical receiving bore, several axially acting cup-spring packages, which cup-spring packages act in a tool clamping sense through several radially extending support arms onto the collet carrier; and by providing in the bore of the tool holder conical shaft at least one hydraulically loadable piston, which acts opposite to the spring pressure on the collet carrier for releasing the collet and ejecting the tool cone.
With the help of the cup-spring packages, which are arranged concentric with the second conical receiving bore and which act onto the collet carrier, a high spring pressure is achieved, which reliably pulls the conical shaft of the tool into the conical receiving bore. By arranging several cup-spring packages in the support member around the second receiving bore, a relatively short axial structural length of the tool holder and a high clamping force are achieved. For the purpose of releasing the collet and for ejecting the tool, a hydraulically loadable piston is provided, which acts against the spring pressure of the cup-spring packages. By arranging this piston and the collet carrier in a bore of the tool holder conical shaft, the available space is well utilized, which also results in a structure of small dimensions in the axial direction. Since for releasing the collet and for ejecting the tool conical shaft only the feeding of a pressure medium to the tool holder is necessary, which can be done for example by a hollow draw rod in the machine tool spindle, and since for clamping the tool conical shaft the axially acting cup-spring packages serve after eliminating the pressure loading on the piston, the new tool holder is suited very well for automatic exchange of smaller tools. The new tool holder itself can also, in a simple manner by means of the draw rod in the machine tool spindle, be pulled into the conical receiving bore of the spindle or be ejected from the spindle and be exchanged for another tool or other mechanism, which if desired can also occur automatically.
In order to assure the desired high clamping forces, it is necessary to provide a correspondingly large number of cup springs in the support member. For releasing the collet, the piston must act against this high clamping force applied by the cup springs. Furthermore, for ejecting a tightly fitting tool conical shaft, the friction forces between said conical shaft and the conical receiving bore must also be overcome. In order to assure here a satisfactory release and ejection function, it is advantageous to permit two pistons which are oriented one after the other to act on the collet carrier.
Therefore, in a further advantageous development of the invention the tool holder conical shaft contains two pistons located axially one after the other. The first piston is supported movably in the bore itself and the second piston is supported movably in a cylinder inserted into the bore. The cylinder has a bottom through which is guided a piston rod of the first piston, which piston rod rests on the second piston. The second piston acts with its piston rod onto the collet carrier.
This orientation of the pistons one after the other permits producing, in the available, relatively small structural space within the tool conical shaft, the necessary ejecting force.
Further advantageous developments of the invention will be discussed in greater detail hereinafter in connection with one exemplary embodiment, which is illustrated in the drawing.